Primary State Highway 10 (Washington)

Marker for PSH 1
Highway names
Primary:	Primary State Highway X (PSH X)
Secondary:	Secondard State Highway X (SSH X)
System links
State highways in Washington Interstate US State Scenic Former PSH 1964 renumbering Former

Primary State Highway 1
Location:	Vancouver to Canada–United States border
Existed:	1937–1964

Primary State Highway 2
Location:	Seattle to Idaho State Line
Existed:	1937–1964

Primary State Highway 3
Location:	Cle Elum to Canada–United States border
Existed:	1937–1964

Primary State Highway 4
Location:	Tonasket to Wilbur
Existed:	1937–1964

Primary State Highway 5
Location:	Seattle to Yakima
Existed:	1937–1964

Primary State Highway 6
Location:	Spokane to Canada–United States border
Existed:	1937–1964

Primary State Highway 7
Location:	Ellensburg to Davenport
Existed:	1937–1964

Primary State Highway 8
Location:	Vancouver to Buena
Existed:	1937–1964

Primary State Highway 9
Location:	Olympia to Mud Bay
Existed:	1937–1964

Primary State Highways were major state highways in Washington state. They were used from 1905 to 1964. The 1964 state highway renumbering changed the highway numbering in the state to consolidate and create a more organized and systematic method of numbering the highways within the state.

The first state road, running across the Cascade Range roughly where State Route 20 now crosses it, was designated by the legislature in 1893 (However, this road wasn't actually opened until 1972). Two other roads - a Cascade crossing at present State Route 410 and a branch of the first road to Wenatchee - were added in 1897. The Washington Highway Department was established in 1905, and a set of twelve State Roads, numbered from 1 to 12, were assigned. A thirteenth was added in 1907, and State Roads 14 to 18 in 1909.

However, it was not until 1913 that a connected system was laid out - earlier state roads had been disconnected segments of road needing improvements. The seven primary roads were only assigned names, while the older state roads kept their numbers as secondary roads. In 1923, most state roads were assigned new numbers, though the primary and secondary split remained, and several roads remained named only. The United States Numbered Highways were assigned in late 1926, overlapping some of the State Roads.

The first major reworking of the system was passed in 1937, including a complete renumbering. A number of Primary State Highways were designated, while Secondary State Highways were suffixed spurs off those. For instance, Primary State Highway 1 was the Pacific Highway (present Interstate 5), and Secondary State Highway 1B was a spur from Bellingham to the Canadian border (now State Route 539). U.S. Routes kept dual designations with State Highways. By 1952, the present highway shield, in the shape of George Washington's head, had been adopted.

...
Wikipedia